Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

magnetic levitation
(1) noncontact support of an object using magnetic forces. Abbreviated as maglev.

(2) a method of melting metals without contacting a surface. A cone-shaped high-frequency coil produces eddy currents in the metal which are strong enough to both suspend and melt it, generally in a neutral atmosphere.

(3) one of several techniques of suspending a driveshaft within a bearing so that no contact is made between the shaft and other surfaces. magnetic bearing

(4) one of several techniques for suspending a railroad train above its tracks so that wheels are not needed. Typically, superconducting magnets are needed, and propulsion is by a linear induction motor cf whose armature lies along the rails.
magnetic loss
losses in magnetic flux in a magnetic circuit, primarily due to magnetic leakage and fringing.
See core loss
magnetic moment
for a current-carrying coil in an external magnetic field, the ratio of the torque sensed by the coil to the flux density of the external field. In permanent magnets, the product of the polar flux and the magnetic length; the product of the intrinsic flux density and the magnet volume.
magnetic monopole
a magnet system that produces a magnetic field of a single polarity. Although nonexistent, may be approximated by one pole of a very long magnet.
magnetic motor starter
motor starter that uses electromechanical devices such as contactors and relays.
magnetic orientation
the preferred direction of magnetization for an anisotropic magnetic material.
magnetic overload
an overload sensor in a motor controller used to shut off the motor in event of an over current condition. With a magnetic overload, the sensor uses a magnetic coil to sense the overload condition, then trips the overload contact(s).
See overload relay
magnetic permeability tensor
relationship between the magnetic field vector and the magnetic flux density vector in a medium with no hysteresis; flux density divided by the magnetic field in scalar media.
magnetic polarization vector
an auxiliary vector in electromagnetics that accounts for the presence of atomic circulating currents in a material. Macroscopically, the magnetic polarization vector is equal to the average number of magnetic dipole moments per unit volume.
magnetic resonance imaging (MRI)
(1) a form of medical imaging with tomographic display that represents the density and bonding of protons (primarily in water) in the tissues of the body, based upon the ability of certain atomic nuclei in a magnetic field to absorb and reemit electromagnetic radiation at specific frequencies. nuclear magnetic resonance

(2) an imaging modality that uses a pulsed radio frequency magnetic field to selectively change the orientation of the magnetization vectors of protons within the object under study. The change in net magnetic moment as the protons relax back to their original orientation is detected and used to form an image.
magnetic saturation
the condition in a magnetic material when an increase in the magnetizing force does not result in a useful increase in the magnetic induction of the material.
magnetic separator
a device employing magnetic fields to separate magnetic materials from nonmagnetic ones.
magnetic stabilization
the act of purposely demagnetizing a magnet with reverse fields or a change in temperature so that no irreversible losses are experienced when the magnet operates under similar conditions in the field.
magnetic susceptibility
the ratio of the magnetization to the applied external field.

Tensor relationship between the magnetic field vector and the magnetization vector in a medium with no hysteresis; magnetization divided by the permeability of free space and the magnetic field in scalar media. It is an indicator of how easily a material is magnetized and has no units in the SI system of units (pure number).
magnetic suspension

See magnetic levitation
magnetic torque coupling
any device utilizing a magnetic field to transmit torque.
magnetic vector potential
an auxiliary field used to simplify electromagnetic computations. This field satisfies a wave equation, the curl of this field is related to the magnetic field intensity vector field, and the divergence of this field is specified by some gage which is to be specified in each problem.
magnetization curve

See hysteresis curve
magnetizing current
the current required to magnetize the different parts of a magnetic circuit. It is calculated as the ratio of the total magnetomotive force (F) and the number of turns (N). More or less in transformers, and AC synchronous and induction machines, the magnetizing current is the current through the magnetizing inductance. Denoted by Im,it is calculated as the ratio of the induced EMF across the magnetizing inductance to its magnetizing reactance Xm.
magneto plasma
a plasma medium that in the presence of a static magnetic field behaves like an anisotropic dielectric medium whose dielectric function is a tensor.